Since the end of World War II, US alliances have been at the core of the regional orders in both East Asia and Western Europe. However, doubts about the US-hegemonic order have arisen due to great power competition and uncertainty about US leadership. This introductory paper sets out the research questions which the papers for this Special Issue address, and discusses key implications of their findings. It suggests the divergent worldviews held by the United States and its allies/partners could create political tensions between them, and also motivate US allies/partners to review the role of these alliances and partnerships within their individual state strategies. If an international order's quality rests on how stable, peaceful, and consensual it is, the choices and actions made by US allies and partners can significantly impact regional dynamics and order-building.